Measuring circuit for a system of electrical modules connected in series

ABSTRACT

A measurement circuit for a system of electrical modules in series with which are associated individual measurement interfaces and a measurement transducer to which the interfaces successively supply their measurement signals via a first serial link in response to interface selection pulses from a common logic unit transmitted serially from one interface to the next via a link. Each measurement signal is transmitted to the transducer either directly for the one closest to the transducer or via one or more interfaces which are not selected and which it crosses, depending on the position within the sequence of interfaces of the interface which produced it. To this end a routing unit, a measurement signal generator and a bypass are associated with each other in each interface. Protective diodes are connected in series in the link elements between the interfaces of two successive modules.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a measuring circuit for a modular system ofelectrical modules connected in series and in particular for a system ofmodules each consisting of one or more elements for producing, storingor converting electrical energy. It is more particularly concerned withsystems comprising multiple modules operating at a high voltage.

2. Description of the Prior Art

The operation of systems of electrical modules connected in series canbe largely optimized, in particular when the number of modules isrelatively large, if it is possible to monitor the operation of eachmodule accurately and consequently to carry out measurements module bymodule.

U.S. Pat. No. 5,638,002 describes a measuring circuit for such systemsof modules. It provides accurate measurements and reduces the number ofelectrical connections needed to transmit measurement signals. A firstserial link connects measurement interfaces individually assigned to themodules and enables a common transducer to handle successivelymeasurement signals obtained by means of current generators at theinterfaces. A second serial link transmits individual selection pulsesto the interfaces from a common logic unit.

In some cases it is beneficial to have a high voltage at the terminalsof a system of modules, for example to drive the motor in an electricvehicle. This has repercussions in terms of the interfaces of themeasurement circuit for a system of modules of this kind, in that theinterface components may be required to withstand a high voltage,possibly as high as the voltage at the terminals of the system, andmalfunctions that can occur during operation of the system of modulescan lead to the occurrence of abnormal voltages and in particularreverse voltages at the input/output terminals of the interfaces.

SUMMARY OF THE INVENTION

The invention therefore proposes a measurement circuit for a modularsystem of modules electrically connected in series, each consisting ofone or more elements for producing, storing or converting electricalenergy, and with which are associated individual measurement interfacesfor each module and a measurement signal transducer to which theinterfaces successively supply their measurement signals via a firstserial link in response to individual interface selection pulsestransmitted from a common logic unit via a second serial link, whereinthe successive interfaces are interconnected by elements of the firstand second links, at least two interfaces corresponding to twosuccessive modules being connected by two link elements, one of which isa first link element and the other of which is a second link element,each incorporating a protective diode connected in series to protectagainst a reverse voltage, in particular in the event of a break in theelectrical continuity between the modules to which the interfacesbetween which the diodes are connected correspond.

The invention also proposes a measurement circuit for a modular systemof modules electrically connected in series, each comprising one or moreelements for producing, storing or converting electrical energy, andwith which are associated individual measurement interfaces for eachmodule and a measurement signal transducer to which the interfacessuccessively transmit, via a serial first link, current measurementsignals that they respectively produce in response to individualinterface selection pulses transmitted from a common logic unit, eachinterface including a selection pulse processing circuit by means ofwhich it is selected, in which circuit, in which the successiveinterfaces are interconnected by elements of the first link, eachinterface includes a device which associates a routing unit controlledby the selection pulse processing circuit with an analog measurementsignal generator and a bypass, the routing unit alternately putting theanalog measurement signal generator and the common measurement signaltransducer into communication via the first link when the interface isselected and the bypass and the measurement signal transducer intocommunication via the first link when the interface is not selected, thebypass then assuring integral transmission of an analog measurementsignal via the interface to the transducer when the signal is receivedfrom another interface upstream of the bypass on the first link relativeto the transducer.

According to one feature of the invention a second serial link transmitsindividual interface selection pulses transmitted by the common logicunit, the first and second links are respectively made up of elementsinserted between two interfaces corresponding to two successive modules,and at least two interfaces corresponding to two successive modules areconnected by two link elements, one of which is a first link element andthe other of which is a second link element, each incorporating aprotective diode connected in series to protect against reverse voltage,in particular in the event of a break in the electrical continuitybetween the modules to which the interfaces between which the diodes areconnected correspond.

The invention, its features and its advantages are explained in thefollowing description, which is given with reference to the accompanyingdrawing.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE of the accompanying drawing is a theoretical circuitdiagram of a modular system of electrical modules in the form of storagebatteries associated with a measurement circuit in accordance with theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The measurement circuit shown in the single FIGURE is designed to beassociated with a modular electrical system 1 made up of a plurality ofmodules 2 connected in series at power transmission terminals, eachmodule conventionally having two terminals denoted “+” and “−”. Eachmodule is made up of a plurality of elements which produce, convert orstore electrical energy, for example, which elements include storagecells, storage batteries and supercapacitors. The system 1 shown is madeup of electrical modules 2 in the form of storage batteries. Forexample, it is an electric vehicle motor power supply system made up of12 volt batteries connected in series to provide a DC operating voltageof several hundred volts. For safety reasons, and because high currentscan be produced in a system of this kind, there is at least one device 3such as a protective fuse and/or an interrupter device between at leasttwo modules of the system, for example between the two modules in themiddle of the series formed by the series-connected modules.

The measurement circuit of the invention collects information relatingto the operation of the modules 2 of the system 1 and determines thevalue of the DC voltage at the terminals of each module, for example. Itincludes individual measurement interfaces 4 for each module of thesystem with which it is associated. The measurement signals obtained atthe interfaces 4 are successively transmitted to a common analog ordigital measurement signal transducer 5 via a serial link M made up ofsuccessive elements between which the interfaces are inserted. Thetransmission of the signals is governed by a logic unit 6 which sendsstreams of individual interface selection pulses over a serial link Lalso made up of successive elements between which the interfaces areinserted.

In the embodiment shown here, the selection pulses from the logic unit 6are successively transmitted from one interface to the next via theelements forming the link L. Each interface includes a selection pulseprocessing circuit 7 which takes account of the first selection pulse ofa stream it receives from the logic unit 6. Other selection pulsesreceived by the processing circuit 7 of an interface in a stream ofpulses are transmitted by that circuit via the link L to the processingcircuit of the next interface.

The processing circuits 7 of the interfaces are not described in moredetail because they are well known in the art, one example beingdescribed in the previously mentioned U.S. Pat. No. 5,638,002.

The selection pulse processing circuit 7 of an interface 4 controls thesupply of the measurement signal produced by the interface to themeasurement signal transducer 5 when it has received an individualselection pulse to that effect. The signal is deemed to be an analogsignal in the remainder of the description. It could be a digital signalsupplied to the measurement transducer, which would then itself bedigital, and based on a measurement performed at a module via theinterface assigned to that module. The logic unit 6 is connected to themeasurement signal transducer in a manner that can be conventional, andis not shown, in order to take account of the measurement signalsobtained, the logic unit using programed logic based on a processor withassociated memories and a clock, for example, in the conventionalmanner.

In the embodiment shown, the selection pulse processing circuit 7operates on an MOS routing unit 9 of a device 8 and the routing unit isassociated with a measurement signal generator 10 and an MOS bypass 11.

The routing unit 9 of a module interface comprises two MOS transistors,for example. The transistors are controlled so that the measurementsignal generator 10 communicates with the measurement signal transducer5 of the circuit via the link M when the interface of the module inquestion is selected and the bypass 11 communicates with the measurementsignal transducer 5 via the same link M when the interface is notselected.

The bypass 11 provides integral transmission of a measurement signal viathe interface to the measurement signal transducer 5 when the interfaceis not selected and the signal it has received comes from anotherinterface which is upstream of it on the first link, relative to thetransducer. The routing unit 9 of the interface then connects the twoelements of the link M between which the interface is inserted.

In the embodiment shown here, each device 8 includes a measurementsignal generator 10 in the form of an analog current generator. Thegenerator modifies the current flowing in the measurement signaltransducer 5 via the link M. The measurement signal generator 10 of aselected interface 4 modifies the current as a function of a measurementperformed at the interface, for example as a function of the voltage atthe terminals of the module to which the selected interface is assigned.

In the embodiment shown, the current produced by a measurement signalgenerator 10 of an interface as a function of a measurement that hasbeen effected is applied to the resistor constituting the measurementsignal transducer 5 when the interface is selected by a pulse and theelement 8 of the interface routes the measurement signal that thecurrent constitutes to the resistor forming the transducer 5. Themeasurement signal then passes through the elements of the link M andthe routing units 9 and bypasses 11 of the interfaces between theselected interface and the measurement transducer 5.

The bypasses 11 of the non-selected interfaces are then switched intothe line by the respective routing units associated with them in theinterfaces. They assure integral transmission of the analog measurementsignal passing through the interfaces incorporating them. In theembodiment described, the resistor forming the measurement transducer 5is connected to a potential V′ slightly higher than the positivepotential V of the system 1 in the case where the analog measurementsignal is supplied by the immediately upstream interface.

According to the invention, a protection diode 12 is inserted into atleast one element of the link M to prevent the application of a highreverse voltage to the interfaces via the link in the event of a breakin the electrical continuity between the modules 2 of the system 1. Whenthe system 1 is operating, it is associated with a load 14 which in someapplications has a low internal resistance, in particular if the load isan electric motor. Accordingly, the voltage which appears in the eventof intentional or accidental breaking of the continuity between themodules 2 is a reverse voltage and can be too high for the interfaces towithstand in the absence of the protective diode. This reverse voltagecan correspond to the nominal voltage of the system 1, i.e. it can beseveral hundred volts.

For a similar reason, a protective diode 12′ is also provided in thelink element L connecting the same interfaces as a link element Mincorporating a protective diode 12.

In the example shown in the single FIGURE, there are protective diodes12 and 12′ in all the link elements L and M connecting two interfaces,although of course the diodes could be provided alternately in theinterfaces with which they are associated. Protective diodes 12 and 12′could instead be provided for a group of interfaces with a minimum ofone diode per link L, M if the reverse voltage that may occur allowsthis. One such limiting case occurs if the series-connected modules 2 ofa system 1 are divided into two sub-systems each corresponding to a bankof storage batteries, for example, and a device 3 including a fuseand/or a disconnector is provided between the two sub-systems. Thediodes 12 and 12′ are then inserted between the two interfaces 4 whichare assigned to the modules 2 each belonging to a different sub-systembetween which the device 11 is located. Other variants are feasible, ofcourse.

The interfaces 4 described here are of the kind described in U.S. Pat.Nos. 5,578,927 and 5,638,002. The measurement generator 10 of eachinterface is based on a circuit for measuring the voltage at theterminals of the module to which the interface is assigned, for example.

There is claimed:
 1. A measurement circuit for a modular system ofmodules electrically connected in series, each consisting of one or moreelements for producing, storing or converting electrical energy, andwith which are associated individual measurement interfaces for eachmodule and a measurement signal transducer to which the interfacessuccessively supply their measurement signals via a first serial link inresponse to individual interface selection pulses transmitted from acommon logic unit via a second serial link, wherein said successiveinterfaces are interconnected by elements of said first and secondlinks, at least two interfaces corresponding to two successive modulesbeing connected by two link elements, one of which is a first linkelement and the other of which is a second link element, eachincorporating a protective diode connected in series to protect againsta reverse voltage, in particular in the event of a break in theelectrical continuity between the modules to which the interfacesbetween which said diodes are connected correspond.
 2. A measurementcircuit for a modular system of modules electrically connected inseries, each comprising one or more elements for producing, storing orconverting electrical energy, and with which are associated individualmeasurement interfaces for each module and a measurement signaltransducer to which the interfaces successively transmit, via a serialfirst link, current measurement signals that they respectively producein response to individual interface selection pulses transmitted from acommon logic unit, each interface including a selection pulse processingcircuit by means of which it is selected, in which circuit, in which thesuccessive interfaces are interconnected by elements of said first link,each interface includes a device which associates a routing unitcontrolled by said selection pulse processing circuit with an analogmeasurement signal generator and a bypass, said routing unit alternatelypuffing said analog measurement signal generator and said commonmeasurement signal transducer into communication via said first linkwhen said interface is selected and said bypass and said measurementsignal transducer into communication via said first link when saidinterface is not selected, said bypass then assuring integraltransmission of an analog measurement signal via said interface to saidtransducer when said signal is received from another interface upstreamof said bypass on said first link relative to said transducer.
 3. Ameasurement circuit as claimed in claim 2 wherein a second serial linktransmits individual interface selection pulses transmitted by saidcommon logic unit, said first and second links are respectively made upof elements inserted between two interfaces corresponding to twosuccessive modules, and at least two interfaces corresponding to twosuccessive modules are connected by two link elements, one of which is afirst link element and the other of which is a second link element, eachincorporating a protective diode connected in series to protect againstreverse voltage, in particular in the event of a break in the electricalcontinuity between said modules to which said interfaces between whichsaid diodes are connected correspond.